Coated tool and cutting tool including the same

ABSTRACT

A coated tool in the present disclosure includes a base and a coating layer located on a surface of the base. The coating layer includes an intermediate layer including Ti, and an Al 2 O 3  layer. The Al 2 O 3  layer is located in contact with the intermediate layer at a position further away from the base than the intermediate layer. The intermediate layer includes a plurality of first protrusions protruding toward the Al 2 O 3  layer. At least one of the plurality of first protrusions is a composite protrusion including second protrusions protruding in a direction intersecting with a protruding direction of the first protrusions. An average number of the second protrusions in the composite protrusion is 1.4 or less. A cutting tool in the present disclosure includes a holder which is extended from a first end toward a second end and includes a pocket on a side of the first end, and the coated tool located in the pocket.

TECHNICAL FIELD

The present disclosure relates to a coated tool including a coating layer on a surface of a base, and a cutting tool including the coated tool.

BACKGROUND

Coated tools, such as cutting tools with a coating layer, have been known in which an Al₂O₃ layer is laminated on a surface of a base of cemented carbide, cermet, ceramics or the like by interposing a bonding film therebetween.

With improved efficiency in recent cutting processes, the cutting tools tend to be increasingly used in, for example, a heavy intermittent cutting process during which a cutting edge is subjected to a large impact. The large impact may be exerted on the coating layer under such severe cutting conditions, and the coating layer may be prone to chipping and peeling off. Hence, the coating layer needs improvement in terms of fracture resistance in addition to wear resistance.

In order to solve the above problem, Patent Document 1 discusses that a protrusion whose tip is bent in a hook shape is located on an interface in contact with the Al₂O₃ layer.

Patent Document 2 and Patent Document 3 discuss that a composite protrusion including a large number of second protrusions is located on a side surface of a first protrusion extending in a laminate direction of a coating layer on an interface in contact with an Al₂O₃ layer.

Of these, the tip of the protrusion discussed in Patent Document 1 and a tip of the composite protrusion discussed in Patent Document 2 have an obtuse angle and such a shape that is poor in film forming properties. In the composite protrusions discussed in Patent Documents 2 and 3, the first protrusion includes the large number of the second protrusions, resulting in the shape having poor film forming properties.

RELATED ART DOCUMENTS Patent Document

Patent Document 1: Japanese Unexamined Patent Publication No. 2004-74324

Patent Document 2: U.S. Unexamined Patent Publication No. 2013/0149527

Patent Document 3: Japanese Unexamined Patent Publication No. 2009-166216

SUMMARY Problems to be Solved by the Invention

The invention provides a coated tool excellent in fracture resistance.

Means for Solving the Problems

A coated tool in the present disclosure includes a base and a coating layer located on a surface of the base. The coating layer includes an intermediate layer including Ti, and an Al₂O₃ layer. The Al₂O₃ layer is located in contact with the intermediate layer at a position further away from the base than the intermediate layer. The intermediate layer includes a plurality of first protrusions protruding toward the Al₂O₃ layer. At least one of the plurality of first protrusions is a composite protrusion including second protrusions protruding in a direction intersecting with a protruding direction of the first protrusions. An average number of the second protrusions in the composite protrusion is 1.4 or less. A cutting tool in the present disclosure includes a holder which is extended from a first end toward a second end and includes a pocket on a side of the first end, and the coated tool located in the pocket.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view illustrating an embodiment of coated tools in the present disclosure;

FIG. 2 is a schematic diagram for describing a configuration of a cross section of a coating layer in the coated tool in FIG. 1;

FIG. 3 is an enlarged view of an important part for describing a configuration in the vicinity of an intermediate layer and an Al₂O₃ layer in a coated tool of the present disclosure;

FIG. 4 is an enlarged view of an important part for describing a configuration in the vicinity of an intermediate layer and an Al₂O₃ layer in a coated tool of the present disclosure;

FIG. 5 is an enlarged view of an important part for describing a configuration in the vicinity of an intermediate layer and an Al₂O₃ layer in a coated tool of the present disclosure; and

FIG. 6 is a plan view illustrating an embodiment of cutting tools in the present disclosure.

EMBODIMENT

<Coated Tools>

In an embodiment illustrated in FIG. 1, a main surface of a coated tool in the present disclosure has an approximately quadrangular planar shape. However, there is no intention to limit to this shape. The coated tool 1 includes a first surface 2, a second surface 3, and a cutting edge 4 located on at least a part of an intersection of the first surface 2 and the second surface 3. The first surface 2 is a surface called a rake surface, and the second surface 3 is a surface called a flank surface. It can also be said that the cutting edge 4 is located on at least the part of the intersection of the rake surface 2 and the flank surface 3.

Referring to a schematic diagram of FIG. 2 illustrating a configuration of a cross section of a coating layer 7 in the coated tool 1, the coated tool 1 includes a base 5 and the coating layer 7 located on a surface of the base 5.

Examples of material constituting the base 5 of the coated tool 1 may include hard alloys, ceramics or metals. Examples of the hard alloys may include cemented carbides containing tungsten carbide (WC), and iron group metal such as cobalt (Co) or nickel (Ni). Other hard alloys maybe Ti-based cermet containing titanium carbonitride (TiCN), and iron group metal such as cobalt (Co) or nickel (Ni). The ceramics maybe Si₃N₄, Al₂O₃, diamond, or cubic boron nitride (cBN). The metals may be carbon steel, high-speed steel or alloy steel. Of these materials, cemented carbide or cermet is suitable for the base 5 if used as the coated tool 1 in terms of fracture resistance and wear resistance.

The coating layer 7 includes an intermediate layer 9 including Ti, and an Al₂O₃ layer 11. The Al₂O₃ layer 11 is in contact with the intermediate layer 9 at a position away from the base 5 in the intermediate layer 9.

The intermediate layer 9 in the coated tool 1 of the present disclosure is a layer including Ti, which may include, for example, TiN, TiC and TiNO. Alternatively, the intermediate layer 9 may include, for example, Ti, C and N. In other words, the intermediate layer 9 may include TiCN crystals. The intermediate layer 9 may include, for example, Ti, C, N and O. In other words, the intermediate layer 9 may include TiCNO crystals. This configuration ensures excellent adhesion properties between the Al₂O₃ layer 11 and the intermediate layer 9.

The coated tool 1 of the present disclosure includes a plurality of first protrusions 13 protruding toward the Al₂O₃ layer 11 as illustrated in FIG. 3.

Each of the first protrusions 13 includes a foot 13 a serving as a start point of protrusion of the first protrusion 13. The first protrusion 13 includes a tip 13 b at a position most away from the base 5. In other words, the first protrusion 13 extends from the foot 13 a toward the tip 13 b. The first protrusion 13 representatively has a triangular shape.

The foot 13 a indicates a position near the base 5 in the first protrusion 13. The foot 13 a may be rephrased as a bottom side of the triangular shape formed by the first protrusions 13.

The first protrusions 13 in the coated tool 1 of the present disclosure are ones in which the tip 13 b has an acute angle and a height of 10 nm or more, and a ratio of an average height of the plurality of first protrusions 13 to an average width of the feet 13 a of the plurality of first protrusions 13 is 0.6 or more as illustrated in FIGS. 3 and 4.

At least one of the first protrusions 13 is a composite protrusion 17 including the second protrusion 15 protruding in a direction intersecting with a protruding direction of the first protrusions 13 in the coated tool 1 of the present disclosure as illustrated in FIG. 3. Alternatively, all the first protrusions 13 maybe the composite protrusions 17 in the coated tool 1 of the present disclosure. Hereinafter, the first protrusion 13 including the second protrusion 15 is also referred to as the composite protrusion 17.

The second protrusions 15 in the coated tool 1 of the present disclosure are ones in which a height from a midportion of the foot 15 a of the second protrusion 15 serving as a start point of the protrusion of the second protrusion 15 to the tip 15 b of the second protrusion 15 is 10 nm or more. In other words, fine irregularities located on a side surface of the first protrusion 13 is not regarded as the second protrusion 15 in the coated tool 1 of the present disclosure.

An average number of the second protrusions 15 included in the composite protrusion 17 is 1.4 or less in the coated tool 1 of the present disclosure. The average number of the second protrusions 15 included in the composite protrusion 17 may be an average value of 50 composite protrusions 17. This configuration ensures excellent film forming properties of the Al₂O₃ layer 11 and excellent adhesion properties between the intermediate layer 9 and the Al₂O₃ layer 11. Because the composite protrusion 17 includes the second protrusion 15, a lower limit value of the average number does not include 1.

The average number of the second protrusions 15 included in the composite protrusion 17 may be 1.2 or less in the coated tool 1 of the present disclosure. This configuration ensures more excellent adhesion properties between the intermediate layer 9 and the Al₂O₃ layer 11.

The average number of the second protrusions 15 included in the composite protrusion 17 may be measured, for example, by taking a photograph through a scanning electron microscope or transmission electron microscope at 30,000× magnification. The number of photographs thus taken may be suitably determined according to the number of the existing composite protrusions 17. Other configuration requirements in the coated tool of the present disclosure may be measured similarly.

A ratio of the average height of the second protrusions 15 to the average width of the feet 15 a of the second protrusions 15 may be larger than the ratio of the average height of the plurality of first protrusions 13 to the average width of the feet 13 a of the plurality of first protrusions 13 in the coated tool 1 of the present disclosure. As used herein, the ratio of the average height of the second protrusions 15 to the average width of the feet 15 a of the second protrusions 15 is a value obtained by dividing an average height from the midportions of the feet 15 a of the second protrusions 15 to the tips 15 b of the second protrusions 15 by the average width of the feet 15 a of the second protrusions 15. This configuration ensures more excellent adhesion properties between the intermediate layer 9 and the Al₂O₃ layer 11.

The ratio of the average height of the plurality of first protrusions 13 to the average width of the feet 13 a of the plurality of first protrusions 13 may be 1.2 or less in the coated tool 1 of the present disclosure. This configuration ensures excellent adhesion properties between the intermediate layer 9 and the Al₂O₃ layer 11.

The ratio of the average height of the plurality of first protrusions 13 to the average width of the feet 13 a of the plurality of first protrusions 13 may be 1.0 or less.

The average width of the feet 13 a of the first protrusions 13 may be 10-50 nm, and the average height of the first protrusions 13 may be 10-60 nm in the coated tool 1 of the present disclosure. This configuration ensures excellent adhesion properties between the intermediate layer 9 and the Al₂O₃ layer 11. Alternatively, the average width of the feet 13 a may be 25-45 nm. The average height of the first protrusions 13 may be 10-50 nm.

An average angle of the tips 13 b of the first protrusions 13 may be 50-90° in the coated tool 1 of the present disclosure. This configuration ensures excellent film forming properties of the Al₂O₃ layer 11 and excellent adhesion properties between the intermediate layer 9 and the Al₂O₃ layer 11. Alternatively, the average angle of the tips 13 b of the first protrusions 13 may be 55° or more. Still alternatively, the average angle of the tips 13 b of the first protrusions 13 may be 80° or less. This configuration ensures excellent film forming properties of the Al₂O₃ layer 11 and more excellent adhesion properties between the intermediate layer 9 and the Al₂O₃ layer 11.

The composite protrusion 17 may include a third protrusion 19 protruding in a direction intersecting with the protruding direction of the second protrusion 15 as illustrated in FIG. 4. This configuration ensures more excellent adhesion properties between the intermediate layer 9 and the Al₂O₃ layer 11. A height of the third protrusion 19 is 10 nm or more. In other words, the fine irregularities located on the side surface of the second protrusions 15 is not regarded as the third protrusion 19 in the coated tool 1 of the present disclosure. The fine irregularities does not substantially contribute to the adhesion properties between the intermediate layer 9 and the Al₂O₃ layer 11.

The coating layer 7 may include a TiN layer 10 a, a first TiCN layer 10 b, a second TiCN layer, the intermediate layer 9 and the Al₂O₃ layer 11 in this order from the base 5 in the coated tool 1 of the present disclosure as illustrated in FIG. 5. This configuration ensures the coated tool 1 having a long life. The first TiCN layer 10 b may be an MT-TiCN layer described later. The second TiCN layer may be an HT-TiCN layer described later. For example, a TiN layer or the like maybe located as a surface layer (not illustrated). The surface layer may be a material other than titanium nitride, such as titanium carbonitride, titanium carboxynitride and chromium nitride. The surface layer may be composed of a colored material so as to have the function of easily distinguishing used and unused cutting edge. The surface layer may have a thickness of 0.1-3.0 μm.

All the first protrusion 13, the second protrusion 15 and the third protrusion 19 may include Ti, C and N, and may have the same composition in the coated tool 1 of the present disclosure. All the first protrusion 13, the second protrusion 15 and the third protrusion 19 may include Ti, C, N and O, and may have the same composition. If the first protrusion 13, the second protrusion 15 and the third protrusion 19 have the same composition, cracking and breakage are less likely to occur between the first protrusion 13, the second protrusion 15 and the third protrusion 19. This leads to higher adhesion properties between the intermediate layer 9 and the Al₂O₃ layer 11 than having different compositions.

The phrase that the first protrusion 13, the second protrusion 15 and the third protrusion 19 have the same composition denotes that a difference in structural component among them is 5% or less.

A compositional difference among them may be 3% or less, or alternatively may be 1% or less.

The first protrusion 13, the second protrusion 15 and the third protrusion 19 are obtainable by using the same gas when depositing the first protrusion 13, the second protrusion 15 and the third protrusion 19.

The first protrusion 13 and the second protrusion 15 may be different in composition, and the second protrusion 15 and the third protrusion 19 may be different in composition.

The first protrusion 13, the second protrusion 15 and the third protrusion 19, which are different in composition, may be deposited using gases different in composition.

The first protrusion 13 may be inclined relative to the first surface 2 of the base 5, instead of being deposited vertical to the first surface 2 of the base 5.

If the intermediate layer 9 has a thickness of 10-35 nm, hardness of the intermediate layer 9 does not deteriorate, and the Al₂O₃ layer 11 has an α-type crystal structure. As used herein, the thickness of the intermediate layer 9 is one which is obtained by excluding the first protrusion 13, the second protrusion 15 and the third protrusion 19.

The intermediate layer 9 may include the following amounts: 30-70 atom % of titanium, 1-70 atom % of carbon, 1-35 atom % of nitrogen and 3-20 atom % of oxygen. The intermediate layer 9 may further include 10 atom % or less of aluminum, or may include 1-10 atom % of components, such as chlorine or chromium. Alternatively, the intermediate layer 9 may include other minor components.

The first protrusion 13, the second protrusion 15 and the third protrusion 19 may have the same composition and may fall within the composition range described above in the coated tool 1 of the present disclosure.

<Manufacturing Method>

The intermediate layer including first protrusions is formable, for example, by deposition with chemical vapor deposition (CVD) method on a surface of a base under the following conditions.

Firstly, the base is set in a chamber of a deposition apparatus, and then deposition is carried out, for example, at a deposition temperature of 900-990° C. and a gas pressure of 15-40 kPa by using a reaction gas whose composition is 3-15 vol % of titanium tetrachloride (TiCl₄) gas, 3-10 vol % of methane (CH₄) gas, 3-50 vol % of nitrogen (N₂) gas, 0.2-1.0 vol % of carbon monoxide (CO) gas, and the rest, namely, hydrogen (H₂) gas. This process is conveniently called a first term process in a deposition process of the intermediate layer. Deposition time in the first term process may be 20-40 minutes. If the nitrogen (N₂) gas of the reaction gas composition is set to 30-50 vol %, an average width of the feet of the first protrusions tends to become larger, and an average height of the first protrusions tends to become smaller. In other words, it is easy to obtain the first protrusions that are thick and short and are less prone to fracture under the above conditions. The deposition time of the first term process is preferably 20-40 minutes. Under the above deposition conditions, it is easy to form the first protrusions in which an average distance between the feet is 70-120 nm.

Second protrusions are formable by lowering the deposition temperature to a range of 900-940° C. without changing a combination of raw material gases in a latter term in the deposition of the intermediate layer. Total deposition time of the former term process and the latter term process may be 30-90 minutes.

The number of the second protrusions tends to increase, and width and height tend to increase by extending the deposition time in the latter term for the intermediate layer deposition, namely, the process of forming the second protrusions. Additionally, it is easy to form the second protrusions whose extending direction is directed toward the base. Third protrusions extending from the second protrusions are formed by further extending the deposition time.

After depositing the intermediate layer, an Al₂O₃ layer may be deposited at a deposition temperature of 900-990° C. and a gas pressure of 5-20 kPa by using a reaction gas whose composition is 3.5-15 vol % of aluminum trichloride (AlCl₃) gas, 0.5-2.5 vol % of hydrogen chloride (HCl) gas, 0.5-5.0 vol % of carbon dioxide (CO₂) gas, 0-1.0 vol % of hydrogen sulfide (H₂S) gas, and the rest, namely, hydrogen (H₂) gas. The Al₂O₃ layer may be composed of α-alumina.

While the embodiment in which the intermediate layer and the Al₂O₃ layer are sequentially deposited on the base has been described above, the coating layer may include a TiN layer, a first TiCN layer and a second TiCN layer in this order from the base. Then, the intermediate layer and the Al₂O₃ layer may be sequentially located on the second TiCN layer. Furthermore, a surface layer including Ti and N may be located on the Al₂O₃ layer.

If depositing the TiN layer on a surface of the base, deposition may be carried out at a deposition temperature of 800-940° C. and a gas pressure of 8-50 kPa by using a reaction gas whose composition is 0.5-10 vol % of titanium tetrachloride (TiCl₄) gas, 10-60 vol % of nitrogen (N₂) gas, and the rest, namely, hydrogen (H₂) gas.

A first TiCN layer and a second TiCN layer may be located on the TiN layer. The first TiCN layer may be a so-called MT (moderate temperature)-TiCN layer. The MT-TiCN layer is formable, for example, by carrying out deposition using a raw material including titanium tetrachloride (TiCl₄) gas, nitrogen (N₂) gas and acetonitrile (CH₃CN) gas at a relatively low deposition temperature, specifically 780-880° C. If the first TiCN layer has a thickness of 2-15 μm, the first TiCN layer has enhanced wear resistance and fracture resistance. Titanium carbonitride crystals included in the first TiCN layer may be columnar crystals that are narrow and long in a thickness direction of the coating layer.

The second TiCN layer may be a so-called HT (high temperature)-TiCN layer. For example, the HT-TiCN layer may be deposited by using, as a raw material gas, titanium tetrachloride (TiCl₄) gas, nitrogen (N₂) gas and methane (CH₄) gas, without using acetonitrile (CH₃CN) gas, in a deposition temperature range of 900-1050° C. The deposition may be carried out at a higher temperature than the first TiCN layer. The second TiCN layer may have a thickness of 10-900 nm.

An interface layer (not illustrated) including the following amounts of 30-70 atom % of titanium, 15-35 atom % of carbon, 15-35 atom % of nitrogen and 2-10 atom % of oxygen may be located between the first TiCN layer and the second TiCN layer. The interface layer may have a thickness of 5-50 nm.

Embodiments of deposition conditions of the first TiCN layer are described below. Deposition may be carried out at a deposition temperature of 780-880° C. and a gas pressure of 5-25 kPa by using a reaction gas whose composition is 0.5-10 vol % of titanium tetrachloride (TiCl₄) gas, 5-60 vol % of nitrogen (N₂) gas, 0.1-3.0 vol % of acetonitrile (CH₃CN) gas and the rest, namely, hydrogen (H₂) gas. By increasing a content ratio of acetonitrile (CH₃CN) gas at a late stage than an early stage, an average crystal width of titanium carbonitride columnar crystals constituting the first TiCN layer can be made larger on a side of the surface than on a side of the base.

Deposition conditions of the second TiCN layer are described below. Deposition may be carried out at a deposition temperature of 900-990° C. and a gas pressure of 5-40 kPa by using a reaction gas whose composition is 1-4 vol % of titanium tetrachloride (TiCl₄) gas, 5-20 vol % of nitrogen (N₂) gas, 0.1-10 vol % of methane (CH₄) gas, and the rest, namely, hydrogen (H₂) gas.

Thereafter, if needed, at least a cutting edge part of a surface of the coating layer thus deposited is subjected to a polishing process. The cutting edge part becomes smooth by the polishing process, and a workpiece is less susceptible to welding, thereby achieving a tool that is more excellent in fracture resistance.

While the coated tools of the present disclosure have been described, the present disclosure is not limited to the above embodiments, and various improvements and changes may be made without departing from the spirit and scope of the present disclosure.

<Cutting Tools>

A cutting tool of the present disclosure is described below with reference to the drawings.

As illustrated in FIG. 6, the cutting tool 101 of the present disclosure is, for example, a bar-shaped body extended from a first end (an upper end in FIG. 6) toward a second end (a lower end in FIG. 6). As illustrated in FIG. 6, the cutting tool 101 includes a holder 105 with a pocket 103 located on a side of the first end (a tip), and the coated tool 1 located in the pocket 103. The cutting tool 101 includes the coated tool 1 and is therefore capable of carrying out a stable cutting process for a long period of time.

The pocket 103 is a part that permits attachment of the coated tool 1. The pocket 103 includes a seating surface parallel to a lower surface of the holder 105, and a constraining lateral surface inclined relative to the seating surface. The pocket 103 opens into a side of the first end of the holder 105.

The coated tool 1 is located in the pocket 103. A lower surface of the coated tool 1 may be in a direct contact with the pocket 103. Alternatively, a sheet (not illustrated) may be held between the coated tool 1 and the pocket 103.

The coated tool 1 is attached to the holder 105 so that at least a part of a ridgeline where the first surface 2 intersects with the second surface 3, which is usable as the cutting edge 4, is protruded outward from the holder 105. The coated tool 1 is attached to the holder 105 by a screw 107 in the present embodiment. Specifically, the coated tool 1 is attached to the holder 105 in such a manner that screw parts are engaged with each other by inserting the screw 107 into a through hole 17 of the coated tool 1, and by inserting a front end of the screw 107 into a screw hole (not illustrated) formed in the pocket 103.

For example, steel and cast iron are usable as a material of the holder 105. Of these materials, highly tough steel may be used.

The present embodiment has illustrated and described the cutting tool 101 for use in a so-called turning process. Examples of the turning process include inner diameter processing, outer diameter processing and grooving process. The cutting tool 101 is not limited to one which is used for the turning process. For example, the coated tools 1 of the above embodiments may be used for cutting tools used in a milling process.

EXAMPLES

Firstly, 6 mass % of metal cobalt powder having a mean particle diameter of 1.2 μm, 0.5 mass % of titanium carbide powder having a mean particle diameter of 2.0 μm, 5 mass % of niobium carbide powder having a mean particle diameter of 2.0 μm, and the rest, namely, tungsten carbide powder having a mean particle diameter of 1.5 μm were added and mixed together in their respective proportions. A mixture thus obtained was molded into a tool shape (CNMG120408) by press molding, followed by debinding and sintering in a non-oxidizing atmosphere, such as an argon atmosphere and nitrogen atmosphere, at 1450-1600° C. for one hour, thereby manufacturing a base composed of cemented carbide. Thereafter, the manufactured base was subjected to brushing, and a part of the base, serving as a cutting edge, was subjected to round honing.

A coating layer was deposited on the base of the cemented carbide by chemical vapor deposition (CVD) method. An intermediate layer and an Al₂O₃ layer were directly deposited on the base in an embodiment in Table 1. A TiN layer was deposited on a surface of the base of the cemented carbide, and a first TiCN layer, a second TiC layer, an intermediate layer and an Al₂O₃ layer were sequentially deposited on the TiN layer in an embodiment of Table 2. Deposition conditions of the intermediate layers of individual samples were presented in Tables 1 and 2. The intermediate layer was deposited using TiCl₄ gas, N₂ gas, CO gas, and H₂ gas. Columns of raw material gases in Tables 1 and 2 indicate vol % of these individual gases. Depositions were carried out in the order of a first term and a latter term under deposition conditions indicated in columns of the first term and the latter term in Tables 1 and 2. In Samples where the deposition conditions are described only for the first term and the column of the latter term is blank, the deposition was carried out under the deposition conditions for the first term while keeping the deposition conditions unchanged.

A deposition temperature of the Al₂O₃ layer was 950° C., and a gas pressure was 7.5 kPa. A reaction gas composition was 3.7 vol % of aluminum trichloride (AlCl₃) gas, 0.7 vol % of hydrogen chloride (HCl) gas, 4.3 vol % of carbon dioxide (CO₂) gas, 0.3 vol % of hydrogen sulfide (H₂S) gas, and the rest, namely, hydrogen (H₂) gas. Deposition time of the Al₂O₃ layer was 380 minutes.

Deposition conditions of the TiN layer in the embodiment in Table 2 are described below. A deposition temperature of the TiN layer was 850° C., and a gas pressure was 16 kPa. A reaction gas composition was 1.0 vol % of titanium tetrachloride (TiCl₄) gas, 38 vol % of nitrogen (N₂) gas, and the rest, namely, hydrogen (H₂) gas. Deposition time was 180 minutes.

Deposition conditions of the first TiCN layer in the embodiment in Table 2 are described below. A deposition temperature was 850° C., and a gas pressure was 9.0 kPa. A reaction gas composition was 4.0 vol % of titanium tetrachloride (TiCl₄) gas, 23 vol % of nitrogen (N₂) gas, 0.4 vol % of acetonitrile (CH₃CN) gas, and the rest, namely, hydrogen (H₂) gas. Deposition time was 400 minutes.

Deposition conditions of the second TiCN layer in Table 2 are described below. A deposition temperature was 950° C., and a gas pressure was 13 kPa. A reaction gas composition was 4.0 vol % of titanium tetrachloride (TiCl₄) gas, 20 vol % of nitrogen (N₂) gas, 8 vol % of methane (CH₄) gas, and the rest, namely, hydrogen (H₂) gas. Deposition time was 80 minutes.

An SEM observation of a cross section including the coating layer of the samples in Tables 1 and 2 was carried out to observe shapes of the first protrusions and the composite protrusions. The results thereof are presented in Tables 1 and 2.

Fracture resistance was evaluated by conducting an intermittent cutting test using the obtained samples under the following conditions. Test results are presented in Tables 1 and 2. The number of impacts (ratio) presented in Tables 1 and 2 is the ratio of the number of the impacts on the individual samples to the number of impacts on Sample No. 1. Samples have more excellent fracture resistance with increasing the number of impacts (ratio).

<Intermittent Cutting Conditions>

Workpiece: chromium molybdenum steel, a steel material with four grooves (SCM440)

Tool Shape: CNMG120408

Cutting Speed: 300 m/min

Feed rate: 0.3 mm/rev

Depth of Cut: 1.5 mm

Others: Using water-soluble cutting fluid

Evaluation Item: Measuring the number of impacts until occurrence of peeling off of the Al₂O₃ layer

TABLE 1 Deposition conditions of intermediate layers Sample Temperature Pressure Time No. TiCl₄ N₂ CH₄ CO H₂ (° C.) (kPa) (min) 1 First term 4.0 20 8 1.40 Rest 970 10 30 Latter term 4.0 20 8 1.40 Rest 940 10 10 2 First term 4.0 40 8 1.40 Rest 970 10 30 Latter term 4.0 40 8 1.40 Rest 940 10 10 3 First term 4.0 40 8 0.45 Rest 970 20 30 Latter term 4.0 40 8 0.40 Rest 940 20 10 4 First term 4.0 40 8 0.45 Rest 970 20 30 5 First term 4.0 40 8 0.45 Rest 970 20 30 Latter term 4.0 40 8 0.30 Rest 940 20 10 6 First term 4.0 40 8 0.45 Rest 970 20 30 Latter term 4.0 40 8 0.20 Rest 940 20 10 7 First term 4.0 40 8 0.40 Rest 970 20 30 Latter term 4.0 40 8 0.30 Rest 940 20 10 8 First term 4.0 40 8 0.40 Rest 970 20 30 Latter term 4.0 40 8 0.20 Rest 940 20 10 9 First term 4.0 40 8 0.20 Rest 970 20 30 Latter term 4.0 40 8 0.20 Rest 940 20 10 10 First term 4.0 20 8 0.05 Rest 970 20 30 Average Average Average Angle of Presence number of width of first height of first Height/width tip of first Height/width or absence Number of Sample second protrusions protrusions of first protrusions of second of third impacts No. protrusions (nm) (nm) protrusions (°) protrusions protrusions (ratio) 1 1.5 20 95 4.75 12 4.10 Present 1 2 1.5 30 65 2.17 26 2.03 Present 1.1 3 1.4 40 45 1.13 48 1.22 Present 1.3 4 — 36 32 0.89 59 — Absent 1.2 5 1.3 40 40 1.00 53 1.18 Present 1.5 6 1.2 40 36 0.90 58 1.10 Present 1.6 7 1.3 36 40 1.11 48 1.22 Present 1.5 8 1.2 36 35 0.97 54 1.15 Present 1.8 9 1.1 32 21 0.66 75 0.90 Present 2.0 10 — 25 35 1.40 39 — Absent 1

TABLE 2 Deposition conditions of intermediate layers Sample Temperature Pressure Time No. TiCl₄ N₂ CH₄ CO H₂ (° C.) (kPa) (min) 11 First term 4.0 20 8 1.40 Rest 970 10 30 Latter term 4.0 20 8 1.40 Rest 940 10 10 12 First term 4.0 40 8 1.40 Rest 970 10 30 Latter term 4.0 40 8 1.40 Rest 940 10 10 13 First term 4.0 40 8 0.45 Rest 970 20 30 Latter term 4.0 40 8 0.40 Rest 940 20 10 14 First term 4.0 40 8 0.45 Rest 970 20 30 15 First term 4.0 40 8 0.45 Rest 970 20 30 Latter term 4.0 40 8 0.30 Rest 940 20 10 16 First term 4.0 40 8 0.45 Rest 970 20 30 Latter term 4.0 40 8 0.20 Rest 940 20 10 17 First term 4.0 40 8 0.40 Rest 970 20 30 Latter term 4.0 40 8 0.30 Rest 940 20 10 18 First term 4.0 40 8 0.40 Rest 970 20 30 Latter term 4.0 40 8 0.20 Rest 940 20 10 19 First term 4.0 40 8 0.20 Rest 970 20 30 Latter term 4.0 40 8 0.20 Rest 940 20 10 20 First term 4.0 20 8 0.05 Rest 970 20 30 Average Average Average Angle of Height/ Presence number of width of first height of first Height/width tip of first width or absence Number Sample second protrusions protrusions of first protrusions of second of third of impacts No. protrusions (nm) (nm) protrusions (°) protrusions protrusions (ratio) 11 1.5 30 130 4.33 13 4.00 Present 1.6 12 1.5 60 120 2.00 28 2.00 Present 1.7 13 1.4 50 65 1.30 42 1.50 Present 2.1 14 - 45 45 1.00 53 - Absent 1.8 15 1.3 50 58 1.16 47 1.25 Present 2.3 16 1.2 50 52 1.04 51 1.10 Present 2.4 17 1.3 45 57 1.27 43 1.30 Present 2.2 18 1.2 45 50 1.11 48 1.15 Present 2.6 19 1.1 40 35 0.88 59 0.90 Present 2.8 20 - 35 50 1.43 39 - Absent 1.3

The coated tools of Samples Nos. 3 and 5 to 9 in Table 1, which were examples of the present disclosure and in which an average number of the second protrusions included in the composite protrusion was 1.4 or less, were excellent in fracture resistance. Samples Nos. 1 and 2 in which an average number of the second protrusions included in the composite protrusion exceeded 1.4 had lower fracture resistance than Samples Nos. 3 and 5 to 9. Samples Nos. 4 and 10 including no composite protrusion also had lower fracture resistance than Samples Nos. 3 and 5 to 9.

The coated tools of Samples Nos. 13 and 15 to 19 in Table 2, which were examples of the present disclosure and in which an average number of the second protrusions included in the composite protrusion was 1.4 or less, were excellent in fracture resistance. Samples Nos. 11 and 12 whose average number of the second protrusions included in the composite protrusion exceeded 1.4 had lower fracture resistance than Samples Nos. 13 and 15 to 19. Samples Nos. 14 and 20 including no composite protrusion also had lower fracture resistance than Samples Nos. 13 and 15 to 19.

DESCRIPTION OF THE REFERENCE NUMERAL

1 coated tool

2 first surface, rake surface

3 second surface, flank surface

4 cutting edge

5 base

7 coating layer

9 intermediate layer

10 a TiN layer

10 b first TiCN layer

11 Al₂O₃ layer

13 first protrusion

13 a foot of first protrusion

13 b tip of first protrusion

15 second protrusion

15 a foot of second protrusion

15 b tip of second protrusion

17 composite protrusion

19 third protrusion

101 cutting tool

103 pocket

105 holder

107 screw 

1. A coated tool, comprising: a base; and a coating layer located on a surface of the base, the coating layer comprising an intermediate layer comprising Ti and an Al₂O₃ layer, wherein the Al₂O₃ layer is located in contact with the intermediate layer at a position further away from the base than the intermediate layer, the intermediate layer comprises a plurality of first protrusions protruding toward the Al₂O₃ layer, at least one of the plurality of first protrusions is a composite protrusion comprising second protrusions protruding in a direction intersecting with a protruding direction of the first protrusions, and an average number of the second protrusions in the composite protrusion is 1.4 or less.
 2. The coated tool according to claim 1, wherein a ratio of an average height of the second protrusions to an average width of feet of the second protrusions is larger than a ratio of an average height of the plurality of first protrusions to an average width of feet of the plurality of first protrusions.
 3. The coated tool according to claim 1, wherein a ratio of an average height of the plurality of first protrusions to an average width of feet of the plurality of first protrusions is 1.2 or less.
 4. The coated tool according to claim 1, wherein an average width of feet of the plurality of first protrusions is 10 nm or more but less than 50 nm, and an average height of the first protrusions is 10 nm or more but less than 60 nm.
 5. The coated tool according to claim 1, wherein an average angle of tips of the plurality of first protrusions is 50-90°.
 6. The coated tool according to claim 1, wherein the composite protrusion comprises a third protrusion protruding in a direction intersecting with a protruding direction of the second protrusions.
 7. The coated tool according to claim 1, wherein the coating layer comprises a first TiCN layer, a second TiCN layer, the intermediate layer and the Al₂O₃ layer in this order from the base.
 8. The coated tool according to claim 1, wherein the intermediate layer comprises C and N.
 9. The coated tool according to claim 8, wherein the intermediate layer further comprises O.
 10. A cutting tool, comprising: a holder extending from a first end toward a second end and comprising a pocket on a side of the first end; and the coated tool according to claim 1 which is located in the pocket. 